Unsymmetrical benzothiadiazole-based random copolymers

ABSTRACT

A random copolymer comprising the monomer units A, B and C. In this random copolymer A comprisesB comprisesand C comprises an aryl group. Additionally, R1 R2, R3 and R4 are side chains independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups. X1 and X2 are independently selected from the group consisting of: H, Cl, F, CN, alkyl, alkoxy, ester, ketone, amide and aryl groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application which claims the benefitof and priority to U.S. patent application Ser. No. 15/644,208 filedJul. 7, 2017, entitled “Unsymmetrical Benzothiadiazole-Based RandomCopolymers,” which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

This invention relates to unsymmetrically substitutedbenzothiadiazole-based random copolymers.

BACKGROUND OF THE INVENTION

Solar energy using photovoltaic effect requires active semiconductingmaterials to convert light into electricity. Currently, solar cellsbased on silicon are the dominating technology due to their highconversion efficiency. Recently, solar cells based on organic materialsshowed interesting features, especially on the potential of low cost inmaterials and processing. Judging from the recent success in organiclight emitting diodes based on a reverse effect of photovoltaic effect,organic solar cells are very promising.

Organic photovoltaic cells have many potential advantages when comparedto traditional silicon-based devices. Organic photovoltaic cells arelight weight, economical in the materials used, and can be deposited onlow cost substrates, such as flexible plastic foils. However, organicphotovoltaic devices typically have relatively low power conversionefficiency (the ratio of photons absorbed to energy generated. This is,in part, thought to be due to the morphology of the active layer. Thecharge carriers generated must migrate to their respective electrodesbefore recombination or quenching occurs. The diffusion length of anexciton is typically much less than the optical absorption length,requiring a tradeoff between using a thick, and therefore resistive,cell with multiple or highly folded interfaces, or a thin cell with alow optical absorption efficiency.

Conjugated polymers are polymers containing π-electron conjugated unitsalong the main chain. They can be used as active layer materials forsome types of photo-electric devices, such as polymer light emittingdevices, polymer solar cells, polymer field effect transistors, etc. Aspolymer solar cell materials, conjugated polymers should possess someproperties, such as high charge carrier mobility, good harvest ofsunlight, good processability, and proper molecular energy levels. Someconjugated polymers have proven to be good solar cell materials.Conjugated polymers are made of alternating single and double covalentbonds. The conjugated polymers have a δ-bond backbone of intersectingsp² hybrid orbitals. The p_(z) orbitals on the carbon atoms overlap withneighboring p_(z) orbitals to provide π-bonds. The electrons thatcomprise the π-bonds are delocalized over the whole molecule. Thesemiconducting properties of the photovoltaic polymers are derived fromtheir delocalized π bonds. The substituents of the polymers also largelyinfluence the electronic properties. The optical bandgap, mobility andthin-film morphology are affected by both the type of functional groupused as a substituent and the bulkiness and length of the side chain.Polymers which have only minor differences in the side chains will havelarge differences in the device performance.

There is a need in the art for polymer solar cells that exhibitincreased power conversion efficiency and fill factor.

BRIEF SUMMARY OF THE DISCLOSURE

A random copolymer comprising the monomer units A, B and C. In thisrandom copolymer A comprises

B comprises

and C comprises an aryl group. Additionally, R1 R2, R3 and R4 are sidechains independently selected from the group consisting of: H, Cl, F,CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups. X1 and X2are independently selected from the group consisting of: H, Cl, F, CN,alkyl, alkoxy, ester, ketone, amide and aryl groups.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefitsthereof may be acquired by referring to the follow description taken inconjunction with the accompanying drawings in which:

FIG. 1 , depicts the reaction of4,7-Dibromo-5-chloro-2,1,3-benzothiadiazole andtributyl(thiophen-2-yl)stannane to produce4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

FIG. 2 , depicts the NMR of4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

FIG. 3 , depicts the reaction oftrimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane and4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole to produce5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

FIG. 4 , depicts the NMR of5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

FIG. 5 , depicts the reaction of5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazoleto4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole.

FIG. 6 , depicts the NMR of4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole.

FIG. 7 , depicts the synthesis of4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole.

FIG. 8 , depicts the NMR of4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole.

FIG. 9 , depicts the synthesis of4-bromo-7-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole.

FIG. 10 , depicts the synthesis of5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

FIG. 11 , depicts the NMR of5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

FIG. 12 , depicts the synthesis of4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole.

FIG. 13 , depicts the NMR of4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole.

FIG. 14 , depicts the reaction of Example 1.

FIG. 15 , depicts the reaction of Example 2.

FIG. 16 , depicts the reaction of Example 3.

FIG. 17 , depicts the reaction of Example 4.

FIG. 18 , depicts the reaction of Example 5

FIG. 19 , depicts a comparison of the UV-vis spectra of Examples 1-5.

FIG. 20 , depicts the reaction of Example 6

FIG. 21 , depicts the effect of the casting solution concentration onExample 6 on the open-circuit voltage of an organic photovoltaic device.

FIG. 22 , depicts the effect of the casting solution concentration onExample 6 on the short-circuit current density of an organicphotovoltaic device.

FIG. 23 , depicts the effect of the casting solution concentration onExample 6 on the fill factor of an organic photovoltaic device.

FIG. 24 , depicts the effect of the casting solution concentration onExample 6 on the power conversion efficiency of an organic photovoltaicdevice.

FIG. 25 , depicts the effect of the annealing temperature concentrationon Example 6 of an organic photovoltaic device.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement orarrangements of the present invention, it should be understood that theinventive features and concepts may be manifested in other arrangementsand that the scope of the invention is not limited to the embodimentsdescribed or illustrated. The scope of the invention is intended only tobe limited by the scope of the claims that follow.

“Alkyl,” as used herein, refers to an aliphatic hydrocarbon chains. Inone embodiment the aliphatic hydrocarbon chains are of 1 to about 100carbon atoms, preferably 1 to 30 carbon atoms, and includes straight andbranched chained, single, double and triple bonded carbons such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,t-butyl, n-pentyl, isopentyl, neo-pentyl, n-hexyl, isohexyl, thenyl,propenyl, butenyl, pentenyl, hexenyl, butadienyl, pentadienyl,hexadienyl, ethynyl, propynyl, butynyl, pentynyl, hexynyl, 2-ethylhexyl,2-butyloctyl, 2-hexyldecyl, 2-octyldedodecyl, 2-decyltetradecy and thelike. In this application alkyl groups can include the possibility ofsubstituted and unsubstituted alkyl groups. Substituted alkyl groups caninclude one or more halogen substituents.

“Alkoxy,” as used herein, refers to the group R—O— where R is an alkylgroup of 1 to 100 carbon atoms. Examples of alkoxy groups include, butare not limited to, methoxy, ethoxy, propoxy (e.g., n-propoxy andisopropoxy), t-butoxy, pentoxyl, hexoxyl groups, and the like. In thisapplication alkoxy groups can include the possibility of substituted andunsubstituted alkoxy groups.

“Alkylthio” as used herein refers to a —S— alkyl group. Examples ofalkylthio groups include, but are not limited to, methylthio, ethylthio,propylthio (e.g., n-propylthio and isopropylthio), t-butylthio,pentylthio, hexylthio groups, and the like. In this applicationalkylthio groups can include the possibility of substituted andunsubstituted alkylthio groups.

“Aryl” as used herein, refers to an optionally substituted, mono-, di-,tri-, or other multicyclic aromatic ring system having from about 5 toabout 50 carbon atoms (and all combinations and subcombinations ofranges and specific numbers of carbon atoms therein), with from about 6to about 10 carbons being preferred. Non-limiting examples include, forexample, phenyl, naphthyl, anthracenyl, phenanthrenyl, pentacenyl,cyclopentane, cyclohexane, imidazoline, pyran, benzodioxanyl,benzodioxolyl, chromanyl, indolinyl, and the like. Aryl groups can beoptionally substituted with one or with one or more Rx. In thisapplication aryl groups can include the possibility of substituted arylgroups (such as heteroaryls), bridged aryl groups and fused aryl groups.

Fill Factor (FF) as used herein, is the ratio (given as a percentage) ofthe actual maximum obtainable power, (P_(m) or V_(mp)*J_(mp)), to thetheoretical (not actually obtainable) power, (J_(sc)*V_(oc)).Accordingly, FF can be determined using the equation:FF=(V_(mp)*J_(mp))/(J_(sc)*V_(oc)) where J_(mp) and V_(mp) represent thecurrent density and voltage at the maximum power point (P_(m)),respectively, this point being obtained by varying the resistance in thecircuit until J*V is at its greatest value; and J_(sc) and V_(oc)represent the short circuit current and the open circuit voltage,respectively. Fill factor is a key parameter in evaluating theperformance of solar cells.

Open-circuit voltage (V_(oc)) as used herein, is the difference in theelectrical potentials between the anode and the cathode of a device whenthere is no external load connected.

Power conversion efficiency as used herein, of a solar cell is thepercentage of power converted from absorbed light to electrical energy.The power conversion efficiency of a solar cell can be calculated bydividing the maximum power point (P_(m)) by the input light irradiance(E, in W/m²) under standard test conditions and the surface area of thesolar cell (A_(c) in m²). standard test conditions typically refers to atemperature of 25° C. and an irradiance of 1000 W/m² with an air mass1.5 (AM 1.5 G) spectrum.

The present application relates to polymeric compounds that can be usedas organic semiconductor materials. The present compounds can have goodsolubility in various common solvents and good stability in air. Whenincorporated into optical or optoelectronic devices including, but notlimited to, photovoltaic or solar cells, light emitting diodes, andlight emitting transistors, the present compounds can confer variousdesirable performance properties. For example, when the presentcompounds are used in a photoactive layer of a solar cell (e.g., bulkheterojunction devices), the solar cell can exhibit very high powerconversion efficiency (e.g., about 7.0% or greater) and very high fillfactor (e.g., about 68% or greater).

The present embodiment describes a random copolymer comprising themonomer units A, B and C. In this random copolymer A comprises

B comprises

and C comprises an aryl group. Additionally, R1 R2, R3 and R4 are sidechains independently selected from the group consisting of: H, Cl, F,CN, alkyl, alkoxy, alkylthio, ester, ketone and aryl groups. X1 and X2are independently selected from the group consisting of: H, Cl, F, CN,alkyl, alkoxy, ester, ketone, amide and aryl groups. The polymers madefrom the random copolymer can be of any grouping such as ABC, ACB, BAC,BCA, CAB or CBA. These random copolymer can then be combined withanother random copolymer to form random polymeric compounds. For exampleit is possible to form a polymer from a two copolymer system of ABCcombined with either ABC, ACB, BAC, BCA, CAB or CBA. It is theorizedthat the randomness of the copolymer provides improved performancecharacteristics such as power conversion efficiency and fill factor. Thelength of the polymers formed from these random copolymer can range fromas little as two copolymers to ten million copolymers.

The monomer C can be an aryl group selected from groups such as abenzodithiophenyl group, a silylene-bithiophenyl group, a carbazolylgroup, and a dibenzosilole group, each of which can be optionallysubstituted as described herein. For example, the benzodithiophenylgroup, the silylene-bithiophenyl group, the carbazolyl group, and thedibenzosilole group can be substituted with one, two, three or foursolubilizing groups. Each solubilizing group can be a linear or branchedaliphatic group (e.g., an alkyl group, an alkenyl group, an alkoxygroup, or an alkylthio group) having 6-20 carbon atoms. In particularembodiments, each solubilizing group can be a branched C6-20 alkyl groupor a branch C6-20 alkoxy group. Other examples of aryl groups such aspolycyclic heteroaryl groups of C can include:

In the above examples W can be C, Si or Se. R′, R″ can be independentlyselected from H, Cl, F, CN, an alkyl group, an alkoxy group, an arylgroup, a C₆₋₂₀ alkyl group, a —O—C₆₋₂₀ alkyl group, a —O—C₆₋₂₀ alkenylgroup, a —O—C₆₋₂₀ haloalkyl group, a —S—C₆₋₂₀ alkyl group, a —S—C₆₋₂₀alkenyl group, a —S—C₆₋₂₀ haloalkyl group, a -thienyl-C₆₋₂₀ alkyl group,a -thienyl-C₆₋₂₀ alkenyl group, and a -thienyl-C₆₋₂₀ haloalkyl group

The formation of the random copolymer of coupling C can be performed byany conventionally known coupling reaction. Examples of differentcoupling reactions that can be used include, Wurtz reaction, Glasercoupling, Ullman reaction, Gomberg-Bachmann reaction, Cadiot-Chodkiewiczcoupling, Pinacol coupling reaction, Castro-Stephens coupling, Gilmanreagent coupling, Cassar reaction, Kumada coupling, Heck reaction,Sonogashira coupling, Negishi coupling, Stile coupling, Suzuki reaction,Hiyama coupling, Buchwald-Hartwig reaction, Fukuyama coupling,Liebeskind-Srogl coupling, Direct Heteroarylation and MacMillancoupling.

It is theorized that the random copolymer structure contributes toincreased power conversion efficiency and increased fill factor.

The polymers or oligomers produced from the present disclosure can beused as part of a photovoltaic material or an active layer material in aphotovoltaic device or an electronic device such as photodetectordevices, solar cell devices, and the like. Photovoltaic devices,including solar cell devices, are generally comprised of laminates of asuitable photovoltaic material between a hole-collecting electrode layerand an electron-collecting layer. Additional layers, elements or asubstrate may or may not be present. In one embodiment the electronicdevices are field effect transistors, light emitting devices, andsensors, electrochromic devices and capacitors.

In one embodiment the molecular complex is used a polymer or oligomerfor organic photovoltaic devices. In this embodiment the organicphotovoltaic device comprises a cathode, disposed over an electrontransport layer, disposed above a polymer or oligomer created from themolecular complex of the present teachings, disposed above an anode. Inthis embodiment the polymer the electron transport layer can comprise(AO_(x))_(yy)BO_((1-y)) with an optional fullerene dopant.

The anode for the organic photovoltaic device can be any conventionallyknown anode capable of operating as an organic photovoltaic device.Examples of anodes that can be used include: indium tin oxide (ITO),fluorine doped tin oxide (FTO), aluminum, silver, gold, carbon, carbonnanotubes, graphite, graphene, PEDOT:PSS, copper, metal nanowires ormeshes, Zn₉₉InO_(x), Zn₉₈In₂O_(x), Zn₉₇In₃O_(x), Zn₉₅Mg₅O_(x),Zn₉₀Mg₁₀O_(x), and Zn₈₅Mg₁₅O_(x).

The cathode for the organic photovoltaic device can be anyconventionally known cathode capable of operating as an organicphotovoltaic device. Examples of cathodes that can be used include:indium tin oxide, carbon, graphite, graphene, PEDOT:PSS, copper, silver,gold, aluminum, metal nanowires.

The electron transport layer of the organic photovoltaic devicecomprises (DO_(x))_(y)EO_((1-y)). In this embodiment, (DO_(x))_(y) andEO_((1-y)) are metal oxides. A and B can be different metals selected toachieve ideal electron transport layers.

In one embodiment D can be aluminum, indium, zinc, tin, copper, nickel,cobalt, iron, ruthenium, rhodium, osmium, tungsten, magnesium, indium,vanadium, titanium and molybdenum.

In one embodiment E can be aluminum, indium, zinc, tin, copper, nickel,cobalt, iron, ruthenium, rhodium, osmium, tungsten, vanadium, titaniumand molybdenum.

Examples of (DO_(x))_(y)EO_((1-y)) include: (SnO_(x))_(y)ZnO_((1-y)),(AlO_(x))_(y)ZnO_((1-y)), (AlO_(x))_(y)InO_(z(1-y)),(AlO_(x))_(y)SnO_(z(1-y)), (AlO_(x))_(y)CuO_(z(1-y)),(AlO_(x))_(y)WO_(z(1-y)), (InO_(x))_(y)ZnO_((1-y)),(InO_(x))_(y)SnO_(z(1-y)), (InO_(x))_(y)NiO_(z(1-y)),(ZnO_(x))_(y)CuO_(z(1-y)), (ZnO_(x))_(y)NiO_(z(1-y)),(ZnO_(x))_(y)FeO_(z(1-y)), (WO_(x))_(y)VO_(z(1-y)),(WO_(x))_(y)TiO_(z(1-y)), and (WO_(x))_(y)MoO_(z(1-y)).

In one embodiment, (DO_(x))_(y)EO_((1-y)) contains from about 10% toabout 25% atomic % of acetate as characterized with x-ray photoelectronspectroscopy.

In one embodiment, the production of (DO_(x))_(y)EO_((1-y)) occurs fromreacting an organic D precursor in the amounts of (1−y); an organic Eprecursor in the amounts of y; and a base in the amount of (1−y) to 1.

Examples of fullerene dopants that can be combined with the electrontransport layer include

and [6,6]-phenyl-C₆₀-butyric-N-2-trimethylammonium ethyl ester iodide.

In the embodiment of

R′ can be selected from either N, O, S, C, or B. In other embodiment R″can be alkyl chains or substituted alkyl chains. Examples ofsubstitutions for the substituted alkyl chains include halogens, N, Br,O, Si, or S. In one example R″ can be selected from

Other examples of fullerene dopants that can be used include:[6,6]-phenyl-C₆₀-butyric-N-(2-aminoethyl)acetamide,[6,6]-phenyl-C₆₀-butyric-N-triethyleneglycol ester and[6,6]-phenyl-C₆₀-butyric-N-2-dimethylaminoethyl ester.

Representative Molecular Complex Synthesis.

The first step involves the synthesis of4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.4,7-Dibromo-5-chloro-2,1,3-benzothiadiazole (2.2 g, 0.007 mol),tributyl(thiophen-2-yl)stannane (2.5 g, 0.007 mol), andtetrakis(triphenylphosphine) palladium (0.387 g, 0.335 mmol) werecombined in a 50 mL Schlenk flask. After the system was placed undervacuum and backfilled with argon three times, 50 mL of anhydrous toluenewas injected. The reaction was heated at 105° C. for 3 days and thencooled to room temperature. The toluene solvent was removed by a rotaryevaporator, and the resulting residue was purified on a silica gelcolumn with hexane/dichloromethane (v/v, 1/1) as the eluent.Recrystallization from the mixture solvent of IPA/methanol produced ayellow crystal as product (1.4 g, 63.0%). FIG. 1 depicts the reaction of4,7-Dibromo-5-chloro-2,1,3-benzothiadiazole andtributyl(thiophen-2-yl)stannane to produce4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole. FIG. 2depicts the NMR of4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

The next step involves the synthesis of5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.Trimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane (2.449 g, 4.644mmol), 4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole 6(1.4 g, 4.221 mmol), Pd₂dba₃ (0.155 g, 0.169 mmol), and P(o-tol)₃ (0.206g, 0.675 mmol) were combined in a 50 mL Schlenk flask. After the systemwas placed under vacuum and backfilled with argon three times, 15 mL ofanhydrous toluene was injected. The reaction was heated at 105° C. for 2days and cooled to room temperature. The toluene solvent was removed bya rotary evaporator, and the resulting residue was purified on a silicagel column with hexane/dichloromethane (v/v, 3/1) as the eluent.Recrystallization from the mixture solvent of IPA/methanol produced ared crystalline product (2.1 g, 80.8%). FIG. 3 depicts the reaction oftrimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane and4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole to produce5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.FIG. 4 depicts the NMR of5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole.

The next step involves the synthesis of4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole.5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole7 (2.09 g, 3.396 mmol) was added to a 100 mL Schlenk flask followed by50 mL of anhydrous THF. The solution was cooled to 0° C. beforeN-bromosuccinimide (1.269 g, 7.132 mmol) was added in portions. Thereaction was stirred overnight. The reaction was stopped by addingsaturated potassium carbonate solution and then extracted with hexane.The combined organic layer was dried over anhydrous MgSO₄. After theremoval of solvent, the resulting mixture was subjected to columnpurification with hexane as the eluent. Red crystal (1.91 g, 72.7%) wasobtained as product after recrystallization in isopropanol and drying invacuo. FIG. 5 depicts the reaction of5-chloro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazoleto4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole.FIG. 6 depicts the NMR of4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole.

Synthesis of4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazoledepicted in FIG. 7 : Trimethyl[4-(2-octyldodecyl)thiophen-2-yl]stannane(1.759 g, 3.334 mmol), 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole(1 g, 3.031 mmol) and tetrakis(triphenylphosphine) palladium (0.175 g,0.152 mmol) were combined in a 100 mL Schlenk flask. After the systemwas placed under vacuum and backfilled with argon three times, 30 mL ofanhydrous toluene was injected. The reaction was heated at 105° C. for48 h and cooled to room temperature. The toluene solvent was removed bya rotary evaporator, and the resulting residue was purified by using asilica gel column with hexane/chloroform mixture (v/v, 95/5) as theeluent. Removal of the solvent finally produced a yellow crystal asproduct (0.2 g, 10.8%). The NMR spectrum is shown in FIG. 8 .

Synthesis of4-bromo-7-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazoledepicted in FIG. 9 :4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole(2.14 g, 3.487 mmol) was added to a 100 mL Schlenk flask followed by 60mL of anhydrous tetrahydrofuran (THF). The solution was cooled to −78°C. before N-bromosuccinimide (0.652 g, 3.661 mmol) was added in portionswith the absence of light. The reaction was stirred overnight. Thereaction was stopped by adding saturated potassium carbonate solutionand then was extracted with hexane. The combined organic layer was driedover anhydrous MgSO₄. After removal of the solvent, the resultingmixture was subjected to column purification with hexane as the eluent.A yellow crystal (0.83 g, 34.3%) was obtained as product afterrecrystallization in iso-propanol at −20° C. and being dried in vacuo atroom temperature.

Synthesis of5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazoledepicted in FIG. 10 :4-bromo-5,6-difluoro-7-[4-(2-octyldodecyl)thiophen-2-yl]-2,1,3-benzothiadiazole(1.916 g, 0.003 mol), tributyl(thiophen-2-yl)stannane (1.282 g, 0.003mol), and Pd₂(dba)₃ (57.177 mg, 0.062 mmol) and P(o-tol)₃ (76.018 mg,0.25 mmol) were combined in a 100 mL Schlenk flask. After the system wasplaced under vacuum and backfilled with argon three times, 20 mL ofanhydrous toluene was injected. The reaction was heated at 105° C. for 2days and cooled to room temperature. The toluene solvent was removed bya rotary evaporator, and the resulting residue was purified by using asilica gel column with hexane/dichloromethane mixture (v/v, 92/8) as theeluent. Recrystallization from the mixture solvent of iso-propanol(IPA)/hexane finally produced a yellow crystal as product (1.65 g,85.9%). The NMR of6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazoleis depicted in FIG. 11 .

Synthesis of4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole,depicted in FIG. 12 :5,6-difluoro-4-(4-(2-octyldodecyl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole(1.62 g, 2.626 mmol) was added to a 100 mL Schlenk flask followed by 50mL of anhydrous tetrahydrofuran (THF). The solution was cooled to −78°C. before N-bromosuccinimide (0.486 g, 2.731 mmol) was added in portionsin dark. The reaction was stirred overnight. The reaction was stopped byadding saturated potassium carbonate solution and then was extractedwith hexane. The combined organic layer was dried over anhydrous MgSO₄.After removal of the solvent, the resulting mixture was subjected tocolumn purification with hexane as the eluent. A orange wax solid (1.36g, 66.9%) was obtained as product after recrystallization iniso-propanol and being dried in vacuo at room temperature. The NMR isdepicted in FIG. 13 .

The following examples of certain embodiments of the invention aregiven. Each example is provided by way of explanation of the invention,one of many embodiments of the invention, and the following examplesshould not be read to limit, or define, the scope of the invention.

Example 1

In a 25 mL Schlenk flask,4-bromo-7-[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole(147.3 mg, 0.213 mmol),(3,3′-difluoro-[2,2′-bithiophene]-5,5′-diyl)bis(trimethylstannane)(35.088 mg, 0.066 mmol), [4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane (111.1 mg, 0.155mmol) and Pd₂dba₃ (4.058 mg, 0.004 mmol) and P(o-tol)₃ (5.395 mg, 0.018mmol) were combined. The mixture was placed under vacuum and backfilledwith argon twice before 2.3 mL of anhydrous chlorobenzene was added. Thesolution was heated to 130° C. for 66 h. The reaction was stopped bybeing cooled to room temperature. The product was precipitated by addinginto methanol and was further purified by Soxhlet extraction, usingacetone (6 h), hexane (24 h), dichloromethane (24 h) and chloroform (16h) as the solvents. The portion obtained from chloroform was the mainproduct (169 mg, yield 90.2%) after precipitation from methanol and thendrying overnight. FIG. 14 depicts the reaction of this coupling.

Example 2

In a 10 mL Schlenk flask,4-bromo-7-[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole(125.498 mg, 0.181 mmol), trimethyl({5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl}) stannane (46.42 mg, 0.094 mmol),[4-(2-hexyldecyl)-5-[5-(trimethylstannyl)thiophen-2-yl]thiophen-2-yl]trimethylstannane(67.6 mg, 0.094 mmol) and Pd₂dba₃ (3.457 mg, 0.004 mmol) and P(o-tol)₃(4.596 mg, 0.015 mmol) were combined. The mixture was placed undervacuum and backfilled with argon twice before 1.9 mL of anhydrouschlorobenzene was added. The solution was heated to 130° C. for 66 h.The reaction was stopped by being cooled to room temperature. Theproduct was precipitated by adding into methanol and was furtherpurified by Soxhlet extraction, using acetone (4 h), hexane (16 h),dichloromethane (4 h), chloroform (4 h) and chlorobenzene (5 h) as thesolvents. The portion obtained from chlorobenzene was the main product(120 mg, yield 81.9%) after precipitation from methanol and then dryingovernight. FIG. 15 depicts the reaction of this coupling.

Example 3

In a 25 mL of Schlenk flask,(4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane)(120.7 mg, 118.707 μmol),4-[5-bromo-4-(2-hexyldecyl)thiophen-2-yl]-7-(5-bromothiophen-2-yl)-5-chloro-2,1,3-benzothiadiazole(81.07 mg, 0.113 mmol), Pd₂dba₃ (2.071 mg, 0.002 mmol), and P(o-tol)₃(5.506 mg, 0.018 mmol) were combined. The mixture was placed undervacuum and backfilled with argon twice before 2.3 mL of anhydrouschlorobenzene was added. The solution was heated at 135° C. for 18hours, and then the mixture was precipitated from methanol after beingcooled to room temperature. The product was precipitated out in 40 mLmethanol and purified by Soxhlet extraction, using acetone (4 hours),hexane (16 hours), and dichloromethane (4 hours) as solvents. Thedichloromethane portion was the main product (99.4 mg, 67.1%) afterprecipitation from methanol and then drying overnight.

Example 4

In a 25 mL Schlenk flask,4-(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole4 (72.4 mg, 0.094 mmol),(4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane)(100.0 mg, 0.098 mmol), Pd2dba3 (3.4 mg, 0.004 mmol), and P(o-tol)3 (4.6mg, 0.015 mmol) were combined. The mixture was placed under vacuum andbackfilled with argon twice before 1.6 mL of anhydrous chlorobenzene wasadded. The solution was heated at 130° C. for 18 hours, and then 20 mLof chloroform was added and the mixture was precipitated from methanol.The product was precipitated out in 40 mL methanol and purified bySoxhlet extraction, using methanol (4 hours), hexane (16 hours), andchloroform (3 hours) as solvents. The chloroform portion was the mainproduct (113 mg, 88.1%) after precipitation from methanol and thendrying overnight. The viscosity in chlorobenzene (10 mg/mL) was 1.105mPa·s at 25.3° C. FIG. 17 depicts the reaction mechanism of thiscoupling.

Example 5

In a 25 mL of Schlenk flask,(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane)(34.482 mg, 0.038 mmol),(4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane)(58.139 mg, 0.057 mmol),4,7-bis[5-bromo-4-(2-octyldodecyl)thiophen-2-yl]-5,6-difluoro-2,1,3-benzothiadiazole7 (106 mg, 0.1 mmol), Pd2dba3 (3.68 mg, 0.004 mmol), and P(o-tol)3 (4.9mg, 0.016 mmol) were combined. The mixture was placed under vacuum andbackfilled with argon twice before 5.0 mL of anhydrous chlorobenzene wasadded. The solution was heated at 130° C. for 18 hours, and then themixture was precipitated from methanol after being cooled to roomtemperature. The product was precipitated out in 40 mL methanol andpurified by Soxhlet extraction, using acetone (4 hours), hexane (16hours), and chloroform (2 hours) as solvents. The chloroform portion wasthe main product (87 mg, 73.0%) after precipitation from methanol andthen drying overnight. The viscosity in chlorobenzene/dichlorobenzene(v/v, 1/1) (10 mg/mL) was 2.058 mPa·s at 25.0° C.

Photovoltaic devices for Examples 1-6 were created using the methodologyof device fabrication below.

Device Fabrication

Zinc tin oxide (ZTO):phenyl-C₆₀-butyric-N-(2-hydroxyethyl)acetamide(PCBNOH) sol-gel solutions were prepared by adding PCBNOH (1.7 mg,2.4×10⁻³ mmol), zinc acetate dihydrate (330 mg, 1.5 mmol), and tin (II)acetate (33 mg, 0.14 mmol) to 2-methoxyethanol (10.6 mL) andethanolamine (92 μL, 1.5 mmol). Solutions were stirred in air for aminimum of 8 h before use. ITO-coated glass substrates were washed withdetergent (2×15 min), DI water (2×15 min), acetone (2×15 min), andisopropanol (2×15 min) in an ultrasonication bath. The substrates wereplaced in an oven at 80° C. for 2+ hours and placed in a UV-ozonecleaner for 1 min. After filtration with a 0.2 μm PVDF syringe filter,ZTO:PCBNOH sol-gel was spin-coated onto the top of the ITO substrate at4000 rpm for 40 s. The substrate was annealed at 210° C. in air for 15min and taken into a glove box for deposition of the active layer. Thephotoactive layer solution was prepared by a 1:1.2 or 1:1.6 polymer:PCBMratio at 14-27.5 mg/mL concentration with 1:1 ratio of chlorobenzene and1,2-dichlorobenzene. See Table I for solution and casting conditions foreach polymer. The solution was mixed in a glove box and heated at 80° C.for 12 hours. Afterward, 2.5 or 3 vol % of 1,8-diiodooctane was added.The photoactive layer solution and ZTO:PCBNOH coated ITO substrates wereheated at 110° C. for 30 min. Spin coating was performed with thephotoactive layer solution, and substrates were heated to 110° C. 80 μLwas pipetted onto the hot substrate and spin coated at 600 rpm or 1000rpm for 40 s, followed immediately by 1200 rpm for 2 s (only for P-27and P-29). The substrates were placed in a closed glass Petri dish for18 hours to allow for solvent annealing. After solvent annealing, thesubstrates were scratched at the edge to expose the ITO layer forcathode electrical connection. The substrates were then placed in themetal evaporator, and 3.5 nm of MoO_(x) and 120 nm of Ag were deposited.The deposition rate for the MoO_(x) was 1.5-2.3 Å/s and Ag was 1.7-2.5Å/s. The devices were encapsulated by using UV-curable epoxy and a coverglass slide and exposed to a UV cure for 3 min.

A comparison of the UV-vis spectra of Examples 1-5 with PCBM is shown inFIG. 19 .

The device performances of Examples 1-5 in a polymer are listed below inTable 1.

TABLE 1 Power Jsc Fill Conversion Polymer Voc (mA/ Factor Efficiency RsRsh Example (V) cm²) % % (Ω cm²) (Ω cm²) 1 0.779 18.84 72.6 10.6 3.51390 2 0.718 19.5 72.3 10.1 3.1 2620 3 0.810 15.5 74.0 9.6 6.8 3000 40.829 17.3 74.3 10.4 3.1 2300 5 0.814 16.2 74.7 9.6 3.2 1900

Example 6

A 500 mL dry Schlenk flask was purged with argon before3-dodecylthiophene (9.79 g, 0.039 mol) andN,N,N′,N′-Tetramethylethylenediamine (TMEDA) (4.96 g, 0.043 mol) wereadded. Anhydrous THF (150 mL) was injected and the resulting solutionwas cooled to −78° C. n-Butyl lithium (2.5 M in hexane, 15.511 mL, 0.039mol) was added dropwise by syringe. The reaction mixture was warmed toroom temperature, and then heated to 60° C. for 1 hour. The reaction wasagain cooled to −78° C. and treated with a trimethyltin chloridesolution (1.0 M in THF, 46.5 mL, 0.047 mol). The reaction was stirredovernight at room temperature. Water (100 mL) was poured into solution,the THF solvent was removed by rotary evaporator, and the aqueous layerwas extracted with hexane (3×100 mL). The combined organic layers werewashed with water (2×) and MeOH (1×) and then dried (Na2SO4), filtered,and concentrated to afford the product (12.8 g, 79.5%) as a colorlessliquid.

(4-dodecylthiophen-2-yl)trimethylstannane (2.26 g, 5.4 mmol),4-bromo-5-chloro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (1.64 g,4.95 mmol), Pd2(dba)3 (0.18 g, 0.20 mmol), and P(o-tol)3 (0.24 g, 0.79mmol) were combined in a 50 mL Schlenk flask. After the system wasplaced under vacuum and backfilled with argon three times, dry toluene(15 mL) was injected. The reaction was heated at 105° C. overnight, andthen cooled to room temperature. The solvent was removed by a rotaryevaporator, and the resulting residue was purified on a silica gelcolumn with hexane/dichloromethane (v/v, 3/1) as the eluent.Recrystallization from a mixture of isopropanol and methanol produced anorange crystalline product (1.81 g, 72.7%).

5-chloro-4-(4-dodecylthiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole(1.81 g, 3.60 mmol) was added to a 100 mL Schlenk flask, followed byanhydrous THF (60 mL). The solution was cooled to −78° C. beforeN-bromosuccinimide (1.34 g, 7.55 mmol) was added in portions. Thereaction was gradually warmed to room temperature and stirred overnight.The reaction was stopped by adding saturated potassium carbonatesolution and then extracted with hexane. The combined organic layerswere dried over anhydrous MgSO4. After the removal of solvent, theresulting mixture was subjected to column purification with hexane asthe eluent. Red crystal (2.0 g, 81.7%) was obtained as product afterrecrystallization in isopropanol and drying in vacuo.

In a Schlenk flask,4-(5-bromo-4-dodecylthiophen-2-yl)-7-(5-bromothiophen-2-yl)-5-chlorobenzo[c][1,2,5]thiadiazole(72.9 mg, 0.11 mmol),4,8-Bis[(2-hexyldecyl)oxy]-2,6-bis(1,1,1-trimethylstannanyl)benzo[1,2-b:4,5-b′]dithiophene(110 mg, 0.11 mmol), P(o-tol)₃ (5.4 mg, 0.018 mmol), and Pd₂(dba)₃ (2.6mg, 2.9 μmol) were combined and degassed for 30 min. After refillingwith argon, dry chlorobenzene (1.8 mL) was added. Two freeze-pump-thawcycles were performed, and the reaction was heated to 120° C. for 24hours. After cooling to room temperature, the polymer was precipitatedin MeOH, and the crude polymer was purified by Soxhlet extraction,washing sequentially with acetone, hexanes, and chloroform. The polymer,Example 6 (85 mg, 81%), was recovered in the chloroform fraction. Thepolymer is depicted in FIG. 20 .

Device Fabrication

The photoactive layer consisted of the donor polymer and acceptor PCBMat a ratio of 1:1.2, respectively. The total solution concentrationranged from 36 to 14 mg/mL in 1:1 o-dichlorobenzene and chlorobenzene.The photoactive layer solution was stirred and heated at 80° C.overnight in a nitrogen filled glove box. The next day, 3 vol % of1,8-diiodooctane (DIO) was added and the solution was heated on the hotplate at 80° C. for an hour. The solution was then filtered with a 2.7μm glass fiber syringe filter.

Indium tin oxide (ITO) patterned glass substrates were cleaned bysuccessive 15 min ultra-sonications in detergent, deionized water,acetone, and isopropanol. The freshly cleaned substrates were left todry overnight at 80° C. Preceding fabrication, the substrates werefurther cleaned for 1 min in a UV-ozone chamber and the electrontransport layer, zinc tin oxide:fullerene, was immediately spin coatedon top.

Single component or mixed metal oxide solutions were filtered directlyonto ITO with a 0.25 μm poly(tetrafluoroethylene) filter and spin castat 4000 rpm for 40 seconds. Films were then annealed at 210° C. for 15min, and directly transferred into a nitrogen filled glove box.

The photoactive layer was deposited from a 110° C. solution ontoITO/ZTO:PCBNOH substrates also at 110° C. The photoactive layer was spincast at 600 rpm for 40 seconds and 1200 rpm for 2 seconds, and directlytransferred into a glass petri dish to solvent anneal for 18+h. Somedevices were thermally annealed on a hot plate after drying for 18+h.After solvent annealing, the substrates were loaded into the vacuumevaporator where MoO_(x) (hole transport layer) and Ag (anode) weresequentially deposited by thermal evaporation. Deposition occurred at apressure of 1×10⁻⁶ torr. MoO_(x) and Ag had thicknesses of 3.5 nm and120 nm, respectively. The deposition rate for the MoO_(x) was 0.6-1 Å/sand Ag was 1.5-2 Å/s. Samples were then encapsulated with glass using anepoxy binder and treated with UV light for 3 min.

Device Testing

Devices with an active area of 0.08306 cm² were tested under AM 1.5 G100 mW/cm² conditions with a Newport Thermal Oriel 91192 1000 W solarsimulator (4″×4″ illumination size). The current density-voltage curveswere measured using a Keithley 2400 source meter. The light intensitywas calibrated with a crystalline silicon reference photovoltaic(area=0.4957 cm²) fitted with a KG-5 filter (calibrated by the Newportto minimize spectral mismatch.

FIG. 21 depicts the effect of the casting solution concentration onExample 6 on the open-circuit voltage of an organic photovoltaic device.

FIG. 22 depicts the effect of the casting solution concentration onExample 6 on the short-circuit current density of an organicphotovoltaic device.

FIG. 23 depicts the effect of the casting solution concentration onExample 6 on the fill factor of an organic photovoltaic device.

FIG. 24 depicts the effect of the casting solution concentration onExample 6 on the power conversion efficiency of an organic photovoltaicdevice.

FIG. 25 depicts the effect of the annealing temperature concentration onExample 6 of an organic photovoltaic device.

The device parameters of Example 6 on different casting solutionconcentrations are listed below in Table 2.

TABLE 2 Concentration Jsc Power Conversion (mg/mL) Voc (V) (mA/cm²) FillFactor % Efficiency % 14 0.75 11.3 76 6.2 17 0.741 11.6 76 6.2 20 0.75614.7 70 7.6 22 0.754 15.1 67 7.4 24 0.750 15.2 67 7.2 28 0.737 16 54 5.932 0.732 14.0 51.9 5.3 36 0.727 11.1 49.5 4.0

The device parameters of Example 6 on different annealing temperaturesare listed below in Table 3.

TABLE 3 Annealing Power Temperature Conversion (° C.) Voc (V) Jsc(mA/cm²) Fill Factor % Efficiency % 25 0.741 13.7 71.9 7.18 40 0.74514.8 73 7.15 60 0.944 14.4 70 7.2 80 0.752 13.0 74 6.9 100 0.759 12.1 746.6

In closing, it should be noted that the discussion of any reference isnot an admission that it is prior art to the present invention,especially any reference that may have a publication date after thepriority date of this application. At the same time, each and everyclaim below is hereby incorporated into this detailed description orspecification as an additional embodiment of the present invention.

Although the systems and processes described herein have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made without departing from the spirit and scopeof the invention as defined by the following claims. Those skilled inthe art may be able to study the preferred embodiments and identifyother ways to practice the invention that are not exactly as describedherein. It is the intent of the inventors that variations andequivalents of the invention are within the scope of the claims whilethe description, abstract and drawings are not to be used to limit thescope of the invention. The invention is specifically intended to be asbroad as the claims below and their equivalents.

The invention claimed is:
 1. A random copolymer comprising monomer unitsA, B and C: wherein A comprises

B comprises

and C comprises an aryl group wherein R1 R2, R3 and R4 are side chainsindependently selected from the group consisting of H, Cl, F, CN, alkyl,alkoxy, alkylthio, ester, ketone and aryl groups; and X1 and X2 areidentical and selected from the group consisting of: H, Cl, F, CN,alkyl, alkoxy, ester, ketone, amide and aryl groups.
 2. The randomcopolymer of claim 1, wherein the molecular weight ranges from 1,000 to100,000 kDa.
 3. The random copolymer of claim 1, wherein C is3,3′-difluoro-2,2′-bithiophene.
 4. The random copolymer of claim 1,wherein when used as a photovoltaic polymer produces a power conversionefficiency greater than 7.0%.
 5. The random copolymer of claim 1,wherein when used as a photovoltaic polymer produces a fill factorgreater than 69%.
 6. The random copolymer of claim 1, wherein R1 and R2are not identical.
 7. The random copolymer of claim 1 wherein Acomprises

B comprises

and C comprises

wherein R3 and R3′ or R4 and R4′ are not equal.
 8. The random copolymerof claim 1, wherein the copolymer contains a unit ABC.
 9. The randomcopolymer of claim 1 wherein the copolymer contains a unit ACB.
 10. Therandom copolymer of claim 1, wherein the copolymer contains a unit BAC.11. The random copolymer of claim 1, wherein the copolymer contains aunit BCA.
 12. The random copolymer of claim 1, wherein the copolymercontains a unit CAB.
 13. The random copolymer of claim 1, wherein thecopolymer contains a unit CBA.
 14. A random copolymer comprising monomerunits A, B and C: wherein A comprises

B comprises

and C comprises an aryl group wherein R1 R2, R3 and R4 are side chainsindependently selected from the group consisting of H, Cl, F, CN, alkyl,alkoxy, alkylthio, ester, ketone and aryl groups; and X1 and X2 are F.